Tool handles



Oct. 1, 1957 c. wHlTEFoRD 2,808,088

Toor. HANDLES Filed June 9, 1955 VF/G. 3.

INVENTOR. N L. WHITEFORD United tats A conventional screwdriver, which consists of a tool comprising a handle, generally of wood, and a steel blade lixed therein, has many uses besides the insertion and withdrawal of screws. In one of its more common uses it is employed with a hammer to drive the blade into articles, such as shipping crates and wooden boxes, to pry them open; and when so used the hammer action on the end of the handle tends to split the handle, or if the latter is of a resilient plastic composition, to drive the blade into and sometimes entirely through the handle. The fact that so many handles are thus injured or destroyed has led to a U. S. governmental regulation that screwdrivers purchased for use by the Army or Navy must be capable of meeting a so-called impact test conducted at room temperature. That test is as follows:

The blade end of each screwdriver shall be mounted vertically in a vise afxed to the base of a suitable falling Weight impact device. The blade tip shall rest on a solid surface to insure that the blade does not move vertically in the vise. The weight shall be 15 pounds, cylindrical in shape, and shall be dropped through a piece of seamless tubing slightly larger than the diameter of the weight in order to insure that the full force of the falling weight will be acting normal to the striking surface. The screwdriver handle shall not break, crack, or signicantly distort, nor shall the blade penetrate more than inch into the handle when the weight has been dropped ten times from the heights listed below. Signicantly distort (for purpose of this test) means an increase of at least 3 percent in the handle diameter, either of a uniform or irregular bulge. In conducting this test, care should be taken that the impact energy shall not be expended in exing of the blade or in driving the screwdriver tip into the surface on which it rests. The blade shall be shortened or blunted, if necessary, to insure a proper test.

Blade diameter: Height of drop of 164 it-pound weight 0.010 for impact test Inches Inches l 1% 52 2% its 7/2 8 V4 10 932 12 5/ s 15 1 lz 17 and over 20 atent 2,808,088 Patented Oct. .1, 1957 ice plastic handle with the shank of the blade inserted and temperature between and 20 F., has high impact n strength and elasticity so as to be momentarilydeformable under high impact, and for which purpose such plastic materials as nylon, ethyl cellulose, cellulose acetate and cellulose acetate butyrate, may be used, for example, l

in practicing my invention. The other piece 15 of the handle assembly consists of a plug having afree t with the inner end of the bore or socket 13; and by free fit I means that while its rounded surface contacts the inner surface of the bore, it does not, like the shank of the blade, fit the bore tightly. The inner end of said plug abuts against the inner end of said bore; and the end of the blade-shank abuts against the other end of said plug. Both the handle proper 14 and the plug 15 may be molded from the same material provided the latter has the properties aforesaid; but for reasons of economy in manufacture I may, for example, mold the handle proper 14 from the relatively less expensive cellulose acetate and the plug 15 from nylon which has the relatively greater impact strength.

After the aforesaid test has been applied to a screwdriver having a handle constructed as hereinbefore described, an examination of the screwdriver will show no measurable penetration of the blade into the handle beyond its original position in the handle, nor any bulge or increase in the handle diameter, although during the test it will be possible to detect a temporary increase in diameter upon each impact, due to the slight expansion of the plug 15 which is indicated by the dotted lines in Fig. 3.

The manner in which the material of the handle assembly responds to each hammer blow on the end of the handle can be the more readily understood if it be assumed that the plug 15 be removed and the place occupied by the plug be filled with a non-compressible liquid, such as oil, and then sealed so that none of the liquid can escape. In such a case, the force of each hammer blow on the end of the handle imparts to the conlined liquid a potential energy, the total amount of which would expend itself not merely against the rear end of the bore or socket 13, but would be evenly distributed over the entire surface of the surrounding plastic material of the handle proper 14, with the result that the handle would slightly expand with each blow and then almost immediately contract to its normal dimensions. Since the solid material of the plug is resilient and thus momentarily deformable under high impact, it can be regarded as flowing at the moment of impact; and, therefore, that the hydraulic principle that liquids under pressure transmit their energy in all directions applies to explainthe reaction of my screwdriver to the impact test aforesaid.

In exploiting my invention, I am at present selling my improved handle assemblies separate from the blades, and which the purchasers thereof use in the manufacture of Screwdrivers by inserting blades of their own manufacture into these handle assemblies.

I claim as my invention:

l. A tool having a steel blade and a handle therefor of a resilient material containing a dead end bore in which the blade is held, the blade having a shank portion-whichis substantially similar in shapeV and size-A to the bore, so as to t tightly in the bore, the inner end of' the shank being spaced from the inner end of the bore, in combination with a flowable material lling the space in said. bore between lthe end Voithegblade ,and the inner end'ofthe bore.

2. In a tool having asteel bladeandra handlefltherefr offa resilient kplastic material of highvimpact strengtlL andelasticity and having a dead endbore inwhieh the shank of the blade is held, the\ shank being substantially similar inrshape and size to the boreand. fitted tightly inthe bore, the combinationrwithA theblade and handle of'a plug falso of a resilient plasticn-materiahofQhigh irn-V` pact strength and elasticity freely` fitted toandfwithinihe. bore of the handle and`against whiehthe bladealutsk 3.' The combination -,oficlaim 2 in Wb'ichaitlfplugis ofthe same plastic Vmaterial as the `said-handle.v

4. The combination of,claim 2 in which, the handle is ofcellulose acetate and the plugofnylon.V Y Y 5. A tool having a blade anda handle ,oflresilient plasticmaterial containing a dead end YboreV in Whieh one. endofithe bladeA is held; the` bore; andthe :eiidlofrthe^ blade held thereby being substantially similar intransverseshapeandVl size and so that the blade is held bya tight fit in the bore, in combination with a solid plugv of resilient plastic material which is substantially similar in transverse shape and size to the bore and the aforesaid end of the blade and which is fitted in the bore between, and in engagement with, the end of the blade and the inner end of the bore.

References Cited in the le of this patent UNITED. STATES PATENTS 628,927 Ducharme July. 18,;,1899

703,457 Perdelwitz .July 1, 1902 1,166,485 Salz Jan. 1, 1916 1,206,014 Massicotte Nov. 28, 1916 1,934,962 Barry Nov. 14, 1933 2,173,942 Hiatt et al Sept. 26, 1939 2,452,100 Campbell Oct. 26, 1948 2,620,001 Fratz Dec. 2, 1952 2,759,734 Velepecl Aug. 2'1, 1956 OTHER: REFERENCES ModernPlastics, page7, April 1497. 

